The expected correlation between polar body twins depends upon the frequency and distribution of chiasmata occurring during oogenesis. We have estimated the expected values of these correlations using assumptions believed to be biologically valid. The expected value of the overall correlation between first polar body twins is estimated to be 0.38 and that between second polar body twins is estimated to be 0.51. There is little difference between the correlation of DZ twins and that expected for second polar body twins. The correlation for a specific locus depends upon its distance from the centromere for both types of polar body twins. This effect is especially marked for second polar body twins. For second polar body twins, loci at or near the telomere will have a correlation close to that expected for first polar body twins. It is concluded that only those markers genes that lie at or close to the centromere are appropriate for the detection of polar body twinning.